As a color conversion method, a method of making color conversion using a look-up table has been proposed. This color conversion method using a look-up table has received a lot of attention since it can freely design (customize) color conversion parameters (e.g., it can convert only local colors on the color space).
However, this color conversion method using a look-up table often generates grayscale discontinuity unless parameters are set after thorough consideration. Especially, in achromatic colors, discontinuity due to tinting of achromatic colors is often perceived due to the human perceptual characteristics.
Conventionally, as an invention that suppresses tinting of achromatic colors upon color conversion, an invention that evenly suppresses chromaticity levels around achromatic colors using a gain or table is known, although it is not a color conversion process using an N-dimensional look-up table. However, such invention cannot cope with subtle hue and luminance changes of achromatic colors of various luminance levels.